Certain vehicles, such as mowers, are used on terrain with variations in slope. These vehicles typically are rated to operate on slopes up to, but not exceeding, a maximum slope. The maximum slope is typically specified in a manual for the vehicle. Some manuals also contain information as to how to manually measure a slope.
One example of a prior art device to assist a driver to assess whether the slope they are driving on is safe is a ball-based visual system mounted to the dashboard of the vehicle where the position of the ball along a path indicates the current angle of the slope across which the vehicle is driving. That is, the device indicates the angle of the slope perpendicular to the direction in which the vehicle is driving.